This invention relates to a plate filter press in which vertically oriented filter plates are horizontally displaceably supported on at least one guide carrier. Each filter plate is provided with at least one fixed projection. The plate filter press has a filter plate shifting device which includes a carrier element which, by means of a drive, is displaceable back and forth in the clearance between the filter plates. The shifting device has a shifting element as well as a reversing element which are both adapted to engage the fixed projection of the filter plate to be displaced from the closed position to the open position (that is, from the closed side to the open side of the filter press).
A plate filter press of the above-outlined type is known and is disclosed, for example, in British Pat. No. 1,422,265. Filter presses equipped with shifting devices of the above-outlined type for the filter plates are, as a rule, operationally reliable. It is, however, a significant disadvantage of the conventional shifting devices that they are of relatively tall construction. Because of the large spatial requirement of the shifting device in the reversing zone, it needs substantial free space and significantly hinders the accessibility of the filter press during discharge or maintenance.
It is a further disadvantage of the prior art structures that the shifting element is moved exclusively by spring force into its abutting relationship with the projection of the filter plate to be displaced so that after extended service, the operational reliability is likely to be adversely affected by soiling, corrosion, or the like.
In plate filter presses in which the individual filter plates are, in the closed state, locked to the adjoining filter plate with locking hooks, the release and shifting of the plates are effected directly with the intermediary of the locking hooks. In instances where after completion of the filtering process significant expansion forces are generated by the filter cakes, the locking hooks too, are exposed to significant corresponding stresses. Since these forces affect the locking hooks in the opening direction, the unlatching of the filter plates from one another has to be carried out under load. The frictional force exerted on the locking hooks thus additionally increases under the effect of the unlatching forces. Consequently, the locking hooks, the release pawls and particularly the springs associated with the respective shifting element of the shifting device have to be of larger dimensions than it would be necessary based on normal force effects. In case of disadvantageous frictional coefficients associated with the interfaces participating in the unlatching operation, the pulling forces increases to such an extent that a secure unlatching cannot always be carried out, thus leading to damages to the entire apparatus.
While the above-outlined known plate filter press construction ensures in principle that an accidental opening of the filter plate stack is prevented, these structures have, however, the further disadvantage that subsequent to unlatching the respective filter plate to be shifted, the latter, because of the kinetic energy, cay by itself continue to move in the transporting direction even after the shifting device is stopped. This circumstance presents high safety risks for the operating personnel.
It is a further disadvantage of the last-named known structure that as the individual filter plate is transported, a disengagement from the shifting element of the shifting device has to occur before the filter plate moves into engagement with that plate which is already in the open position and with which the plate in motion is again to be interlocked. A satisfactory functioning of this motional sequence is therefore dependent from the kinetic energy of the filter plate and the frictional forces opposing the same. If, due to soiling or a premature unlatching of the plate from the shifting element of the shifting device, the frictional forces are greater than the kinetic energy of the plate, the latter will not arrive into engagement with the filter plate stack at the open side of the apparatus so that the intended locking of the filter plate to the filter plate stack at the open side cannot take place.